The network tells TMZ ... Lisa Vanderpump will be back for the new season, but will be surrounded by a new group of staffers who work at her West Hollywood hot spot, SUR.

Season 12 returns to the show's original formula, which takes viewers back inside LVP's many restaurants -- where several hookups, feuds and drama are known to unfold.

Sources connected with the show tell TMZ ... stars Tom Sandoval, Tom Schwartz, Ariana Madix, Scheana Shay, James Kennedy, Katie Maloney, and Lala Kent were notified of this decision by production last night.

We're told most of the cast wasn’t too surprised by the new direction ... especially after the show was put on pause back in April.

Despite the shakeup, our sources say the OG stars will still have a home at the network ... as there will be other avenues for them to explore within the Bravo/NBC universe. We're told Lala, Scheana (as well as hubby Brock Davies), and Schwartz are all making appearances on season 2 of "The Valley" -- a spin-off already starring other 'VPR' alums.

Lala responded to the news by releasing a statement on Instagram, where she noted she was "unbelievably grateful for every moment."

TMZ broke the story ... production had picked up cameras in September to film new faces, all of whom were SUR-vers at Vanderpump's business. At the time, sources said the footage was meant for a new project ... but it's clear Bravo decided to pursue this cast over the OGs for season 12.